US4304458A - Arrangement for displaying deformations of deformable structures by holographic interferometry - Google Patents
Arrangement for displaying deformations of deformable structures by holographic interferometry Download PDFInfo
- Publication number
- US4304458A US4304458A US05/887,341 US88734178A US4304458A US 4304458 A US4304458 A US 4304458A US 88734178 A US88734178 A US 88734178A US 4304458 A US4304458 A US 4304458A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/021—Interferometers using holographic techniques
Definitions
- This invention relates to arrangements for displaying deformations of deformable structures by holographic interferometry.
- Holographic systems can be used for the non-destructive testing of mechanical components placed under stress, observation of the deformations being rendered possible by the memory effect in holographic media.
- the recording of two successive wave fronts with the same reference beam and the restoration by that reference beam of the recorded fringes enables an interference pattern corresponding to the deformations to be created.
- the location of the fringes is directly associated with the deformations which have taken place between the two recorded states.
- Conventional display systems based on holographic interferometry use as their recording medium high-resolution photographic supports which necessitate chemical development and extremely accurate repositioning after the first recording. It is not possible with arrangements using recording materials such as these to follow the deformations of the structures, particularly when the structures in question are vibrating structures.
- an arrangement for displaying deformations of deformable structures by holographic interferometry comprising an electro-optical and photoconductive recording material in which an interferometric hologramme corresponding to the deformations is recorded, polarising means for applying to said material an electrical field orthogonal to the mean direction of the interference fringes to be recorded, and displaying means for forming images of said deformations from said holographic interferogramme.
- FIG. 1 shows a first embodiment of the display arrangement for an object which transmits light, interferometry being obtained by double exposure.
- FIG. 2 is a curve representing the variations in the efficiency of diffraction as a function of the exposure time.
- FIG. 3 shows the control signals applied to the shutters for the object beam, the reference beam and the transmitted beam of the arrangement shown in FIG. 2.
- FIG. 4 shows a second embodiment of the display arrangement for a transmissive object, interferometry being obtained by double exposure.
- FIG. 5 shows a third embodiment of the display arrangement according to the invention for a vibrating reflective object, interferometry being obtained by prolonged exposure relative to the period of vibration.
- FIG. 6 shows a compact embodiment of the display arrangement.
- FIG. 7 shows another embodiment of the polarising means on the recording crystal.
- FIG. 1 shows the layout of the arrangement for displaying a deformable object 1 by holographic interferometry.
- This object is illuminated in a first phase by an object beam 2 issuing from a laser type source 3.
- This object beam may be masked by means of a shutter 4 situated in its path between two lenses 5 and 6.
- the beam 2 diffracted by the transmissive object 1 is directed towards a thick, electro-optical and photoconductive recording material 7.
- This material may be for example a Bi 12 SiO 20 crystal or a Bi 12 GeO 20 crystal, because crystals such as these have good optical qualities, high sensitivity (equivalent to that a high-resolution photographic plates) and a relatively low recording energy of the order of one millijoule per square centimeter for a recording beam supplied by an argon laser source.
- the efficiency of diffraction under an applied field of 6 KV/cm may reach 10% and erasure only requires an exposure energy and time comparable with those required for recording.
- the number of recording-reading cycles in materials of this type is not limited. Finally, it is possible to obtain such crystals in sufficiently large dimensions for the applications envisaged.
- the crystal is subjected to an electrical field E of the order of 6 KV/cm.
- two electrodes 8 and 9 are placed on two parallel faces of the crystal connected to the two terminals of a voltage generator 10.
- a separation plate 16 situated in the path of the beam provides for the formation of a parallel reference beam 11 which is also directed towards the recording medium by means of two return mirrors 12 and 19.
- a shutter 18 placed in the path of the reference beam enables this beam to be masked.
- the plane containing the optical axes of the object and reference beams is parallel to the electrodes carried by the crystal so that the electrical field E is orthogonal to the interference fringes.
- the field E is preferably applied parallel to a preferential axis of the crystal along which the transfer of charges is readily accomplished.
- a lens 13, a shutter 14 and a memory tube 15 capable of recording images are placed along the axis of the object beam.
- the images in question may then be shown on a screen 22.
- the arrangement operates as follows: in a first phase, the object 1 is exposed to the object beam 2 and the wave front diffracted by that object is received by the crystal at the same time as the reference wave.
- the exposure time t o is such that the corresponding figure is recorded to saturation, i.e. the maximum diffraction efficiency ⁇ s is reached.
- the curve of FIG. 2 shows this diffraction efficiency ⁇ as a function of the exposure time.
- the shutter 14 is closed and the shutters 4 and 18 are open.
- a second phase the object 1 is re-exposed to the object beam, the radiation diffracted by the object and the reference beam interfere.
- the exposure time during this second phase is selected in such a way that the first interference figure recorded is only semi-erased so that, during the third phase which is the reading phase, the restored radiations corresponding to the two successive images of the object interfere and the contrast of the fringes is maximal.
- the second phase therefore has a duration around to/2.
- the reading phase Since reading is destructive, the reading phase must not exceed to/2, at the end of which time the crystal returns to its initial state. During this reading phase, the shutters 14 and 18 are open and the shutter 4 is closed. The corresponding pattern is recorded on the memory tube 15 and may then be projected onto the screen 22.
- the blanking functions of the shutters 4, 14 and 18 for the object beam, the reference beam and the restored beam as shown in FIG. 3 may be performed by electrically controlled electro-optical devices using for example crystals of lithium niobate or KDP. Since the object is not permanently illuminated by the object beam in an arrangement such as this, it is possible, as shown in FIG. 1, to use the same reference beam for recording and reading, the restored interferometric image being in no way fogged by the direct object beam transmitted by the recording medium because this beam is masked during reading. An arrangement such as this enables the deformation of a moving object to be observed because, since the exposure time to is of the order of 40 ms, the appearance frequency of the interferogrammes when the shutting functions are automated is compatible with a television scan.
- the image formed is a virtual image and, if it has to be shown on a screen, a convergent lens 13 as described has to be used so as to form a real image.
- the display arrangement based on double exposure holographic interferometry which is shown in FIG. 4 enables a real image to be formed during reading so that there is no need for a convergent system in the path of the restored beam.
- the same elements as in FIG. 1 have been denoted by the same reference numerals.
- the transmissive object 1 is illuminated by the object beam 2 coming from the source 3 when the shutter 4 placed between the two lenses 5 and 6 is open.
- the beam diffracted by the object is received by the crystal 7 carrying the electrodes 8 and 9 connected to the terminals of the voltage generator 10.
- the crystal is also illuminated by the reference beam 11 issuing from the same source by means of a separation plate 16 and a system of return mirrors 12 and 19 when the shutter 18 is open.
- the arrangement additionally comprises for restoration a return mirror 20 orthogonal to the reference beam transmitted by the recording crystal intended to return the light towards the crystal.
- the inverse return of the light thus obtained enables a beam forming a real image to be restored.
- This image is separated from the real object by means of a separation plate 21 and is formed in the conjugate plane P of the object relative to the plate 21.
- This image may be viewed directly in the plane P or may be recorded in the memory tube 15 by means of an optical system 23 to enable it to be subsequently projected onto a screen 22.
- a quarter wave plate 24 may be arranged in the path of the reference beam between the mirror 20 and the crystal 7 to reduce the optical noise introduced by reflection, and a polariser 17 may be placed in the path of the restored beam after the separation plate 21 in order to isolate the interferometric image formed from parasitic illumination because the polarisation state of the diffracted beam during reading is different from that of the recording beams due to the birefractive effect and the rotatory power of the crystal.
- the arrangement shown in FIG. 4 forms an interferometric image of the deformations occurring between two exposures and functions in the same way as the arrangement described with reference to FIG. 1.
- a first exposure of duration to corresponds to the recording of a first interference figure and a second exposure with a duration of around to/2 corresponds to the recording of a second interference figure.
- the display arrangements operating by double exposure holographic interferometry shown in FIGS. 1 and 4 are intended for displaying the deformations of transmissive objects. It is possible to use similar systems for reflecting objects. In this case, the object beam is directed towards the object 1 so that the light diffracted by the object is received by the recording material.
- FIG. 5 Another display system based on holographic interferometry may be used for testing objects subjected to a rapid periodic movement.
- This arrangement is shown in FIG. 5 for an at least partly reflecting object.
- a source 3 emits a laser beam from which the object radiation beam 2 and the reference beam 11 are formed.
- the object radiation is diffracted by a vibrating reflective object 1 denoted by a solid line in one end position, the middle position and the other end position being denoted by dotted lines.
- the amplitude of the vibration is ⁇ e.
- the optical wave diffracted by the vibrating object is received by the recording material 7 after having passed through the partially transparent plate 21 and a convergent lens 6.
- the reference beam is also received by the recording material.
- the exposure time required to obtain saturation efficiency is of the order of 40 to 50 ms.
- the image thus obtained during reading therefore corresponds to the image of the object to be analysed modulated by black fringes corresponding to the zeros of Bessel's function ##EQU2##
- an acousto-optical device 30 (shown in dotted lines in FIG. 5) is placed in the path of the reference beam. This device is intended to introduce into the reference beam of pulsation ⁇ o a frequency shift amounting to a multiple of the vibration frequency of the object to be analysed. If ⁇ v is the pulsation of the object to be analysed, the restored image will comprise black fringes corresponding to the zeros of the Bessel function ##EQU4## for a reference beam of pulsation ( ⁇ o + ⁇ v ) and black fringes corresponding to the zeros of the Bessel function ##EQU5## for a reference beam of pulsation ( ⁇ o +2 ⁇ v ).
- a holographic observation arrangement such as this operating by time-average holographic interferometry enables the vibration amplitudes of vibrating reflective surfaces to be measured with the precision afforded by interferometry and avoids the use of sensitive elements placed in contact with the vibrating surface.
- a thick electro-optical and photoconductive material such as a crystal of Bi 12 SiO 20 or Bi 12 GeO 20
- the invention is not limited to the embodiments of the display arrangements described and illustrated.
- the display systems shown in FIGS. 4 and 5 may comprise, for forming a reading beam directed oppositely to the reference beam, an auxiliary source having the same wavelength as the reference beam in place of the return mirror 20.
- the display arrangement shown in FIG. 6 is a compact arrangement comprising on the one hand a holographic display head and on the other hand optical source means.
- the propagation of the beam issuing from the source is guided in optical cables.
- the laser source may be situated remote from the object whose deformations it is desired to follow and even in another room.
- an arrangement of that type eliminates the need for the usual mechanical adjustments necessitated by the presence of lenses or mirrors and, more generally, of discrete elements in the path of the beam.
- the object 1 to be analysed is illuminated by an object beam 2.
- the object diffracts the beam and an object wave ⁇ O emerges from the object.
- This wave is received by an electro-optical, photoconductive recording material 7.
- This material may be for example a crystal of Bi 12 SiO 20 or CdS.
- the recording material is also illuminated by a reference beam 11.
- the object beam and the reference beam are emitted by optical cables connected to the laser source 3, the reference beam having a spherical wave surface.
- the mirror 200 which is intended to reflect the reference wave surface without deforming it to enable the diffracted image to be permanently viewed is a spherical mirror.
- the quasi-punctiform source formed by the emissive surface of the optical cable emitting the reference wave is placed at the centre of curvature of the spherical mirror 200.
- the electro-optical photoconductive crystal is provided with electrodes 7 and 8 connected to the two terminals of a voltage source 10 which enables an electrical field orthogonal to the mean direction of the interference fringes to be applied to the crystal, so that the crystal is in a transverse electro-optical configuration.
- the electrical field applied may be of the order of 3 to 6 KV/cm.
- the electrical field applied may be of the order of 3 to 6 KV/cm.
- One such mode of application of the electrical field is illustrated in FIG. 7, the electrodes 80 and 90 being in the form of interdigital combs. Since the image is diffuse, the interdigital combs do not affect the restored interferogramme.
- the optical head of the system comprises the laser source 3, a separating plate 16, a lens 35 and two beam shutters 4 and 18.
- the laser source may be of the argon laser or YAG laser type doubled in frequency. These two types of laser emit a visible beam in the sensitivity range of the recording crystal.
- the beam emitted by the laser is received by the separating plate 16 which reflects part of the beam and directs it towards the entry face of an optical cable 36 intended to transmit the object beam. That part of the beam which is transmitted by the separating plate 16 is received by the lens 35 after having passed through the shutter 18.
- This lens focusses the beam onto the entry face of a monomode optical fibre 37 intended to transmit the reference beam.
- This optical reference fibre 37 is monomode so that the wave surface of the beam entering the fibre is not deformed and it is possible to obtain at the exit end of this fibre a point source forming a spherical wave surface.
- the diffracted object wave contains only part of the beam received by the object. Accordingly, to ensure that the contribution of the object and reference beams on the crystal is approximately the same, the separating plate 16 is such that the object beam has a greater intensity than the reference beam.
- the illumination of the object by the object beam is not critical insofar as, even if the optical object cable moves slightly and if the illumination is not uniform, an object wave will nevertheless be emitted towards the recording crystal.
- the system comprises an enclosure 30 in which the various elements are arranged.
- This enclosure comprises a transparent face 31 through which the object wave enters the enclosure.
- the optical reference cable is rigidly fixed to the enclosure by a connecting element 32.
- the recording crystal is also fixed to the enclosure and the connection of the electrodes carried by the crystal to the voltage source 10 is established on the one hand by a direct connection to the enclosure, the enclosure being earthed, and on the other hand by a connection connected to the positive terminal of the voltage source, this connection passing through the enclosure in an insulating joint 33.
- the enclosure also comprises a separating plate 21 and, in the path of the restored beam, a lens 23, a polariser 17 and the image-storing tube 15. The lens enables the size of the restored image to be adapted to the diameter of the vidicon tube used for detection.
- the polariser 17 is oriented in such a way as to isolate the restored image from the optical noise, if any, introduced by the incident object and reference beams.
- the separating plate 21 is placed as close as possible to the recording crystal and may even be fixed to the crystal in such a way that the system is as compact at possible.
- the reference beam has to comply with another characteristic which is to maintain the initial mode so as to form a real source spot.
- One solution to this problem is to use monomode fibres as mentioned above.
- fibres such as these have a relatively small core diameter (of the order of 3 ⁇ m) and only a small opening. Accordingly, the coupling effectiveness of the beam issuing from fibres of this type may be relatively reduced for the application in question.
- Low-loss index-gradient fibres of the type currently available are also suitable for the application in question. Their diameter may vary between 40 and 100 ⁇ m. Fibres of this type enable a point source to be formed and the fibre is arranged in such a way that this point source is situated at the centre of curvature of the spherical mirror.
- the arrangement thus completed forms a self-contained "halographic camera" which is connected to the laser source by optical cables and which may be placed in any interference field.
- the wavelengths selected for the radiation used are in the sensitivity range of the electro-optical photoconductive crystal, i.e. between 350 nm and 550 nm.
- This crystal may either be a thick material (thickness of the order of 2 to 3 mm) or a thin material (thickness of the order of 100 to 200 ⁇ m). With a thin material, it is possible to re-read the hologramme by changing wavelength.
- a system such as this may be used for the non-destructive examination of moving objects or objects subjected to a slow periodic movement. Since interferometry is effected by double exposure, the arrangement operates in the same way as the arrangement described with reference to FIG. 1.
- optical object cable has been shown in position for illuminating a reflective object, although it is equally possible to form a hologramme by illuminating a transmissive object.
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Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR7708627A FR2385079A1 (fr) | 1977-03-23 | 1977-03-23 | Dispositif de visualisation, par interferometrie holographique, des deformations de structures deformables |
FR7708627 | 1977-03-23 |
Publications (1)
Publication Number | Publication Date |
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US4304458A true US4304458A (en) | 1981-12-08 |
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ID=9188447
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US05/887,341 Expired - Lifetime US4304458A (en) | 1977-03-23 | 1978-03-16 | Arrangement for displaying deformations of deformable structures by holographic interferometry |
Country Status (5)
Country | Link |
---|---|
US (1) | US4304458A (de) |
JP (1) | JPS53119078A (de) |
DE (1) | DE2812956A1 (de) |
FR (1) | FR2385079A1 (de) |
GB (1) | GB1599966A (de) |
Cited By (17)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4352566A (en) * | 1980-06-19 | 1982-10-05 | Bell Telephone Laboratories, Incorporated | Detection of birefringence in irregularly shaped objects |
US4442455A (en) * | 1980-05-08 | 1984-04-10 | Thomson-Csf | Optical system for observation in real time with scanning |
US4492468A (en) * | 1980-11-25 | 1985-01-08 | Thomson-Csf | Interferometer for the real time display of deformations of vibrating structures |
US4542955A (en) * | 1982-06-18 | 1985-09-24 | Thomson-Csf | Device for illuminating an electro-optical medium for recording holograms in real time |
US4571080A (en) * | 1981-11-09 | 1986-02-18 | Thomson-Csf | Michelson interferometer with a photorefractive mirror |
US4603096A (en) * | 1984-12-21 | 1986-07-29 | Agency Of Industrial Science & Technology | Hologram recording material |
US4788428A (en) * | 1985-03-04 | 1988-11-29 | The United States Of America As Represented By The Secretary Of The Navy | Thermodynamics infrared imaging sensor |
DE3720142A1 (de) * | 1987-06-16 | 1988-12-29 | Rottenkolber Holo System Gmbh | Holographische messeinrichtung |
US4987545A (en) * | 1986-05-20 | 1991-01-22 | Ingegerd Dirtoft | Method for monitoring the manufacture of a product |
US5049963A (en) * | 1989-03-24 | 1991-09-17 | Matsushita Electric Industrial Co., Ltd. | Holographic television apparatus with semiconductor device |
US5410406A (en) * | 1993-02-01 | 1995-04-25 | Holographics Inc. | Method and apparatus for nondestructive inspection utilizing phase integration and recording of induced vibrating nodal patterns |
US5479257A (en) * | 1993-04-05 | 1995-12-26 | Olympus Optical Co., Ltd. | Method of and apparatus for detecting object position using a fourier transform of the object image and processing system using the same |
US5684588A (en) * | 1996-10-04 | 1997-11-04 | United States Of America As Represented By The Secretary Of The Air Force | Homodyne and hetrodyne imaging in a light scattering medium |
US5827971A (en) * | 1996-05-31 | 1998-10-27 | Lockheed Martin Idaho Technologies Company | Optical vibration detection spectral analysis assembly and method for detecting vibration in an object of interest |
US6134006A (en) * | 1998-02-25 | 2000-10-17 | Becthel Bwxt Idaho, Llc | Imaging photorefractive optical vibration measurement method and device |
US6246521B1 (en) | 1996-11-05 | 2001-06-12 | Thomson-Csf | Compact lighting device |
US20070052969A1 (en) * | 2003-09-26 | 2007-03-08 | Thales | Sensor device used to detect interferometric rotational speed and comprising an optical fibre |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH0682102B2 (ja) * | 1987-02-27 | 1994-10-19 | 三菱電機株式会社 | パターン欠陥検査装置及びパターン欠陥検査方法 |
DE3718327A1 (de) * | 1987-06-01 | 1988-12-22 | Rottenkolber Holo System Gmbh | Vorrichtung zur durchfuehrung von holographischer interferometrie |
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1978
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- 1978-03-21 GB GB11248/78A patent/GB1599966A/en not_active Expired
- 1978-03-23 JP JP3355178A patent/JPS53119078A/ja active Pending
- 1978-03-23 DE DE19782812956 patent/DE2812956A1/de active Granted
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Cited By (18)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4442455A (en) * | 1980-05-08 | 1984-04-10 | Thomson-Csf | Optical system for observation in real time with scanning |
US4352566A (en) * | 1980-06-19 | 1982-10-05 | Bell Telephone Laboratories, Incorporated | Detection of birefringence in irregularly shaped objects |
US4492468A (en) * | 1980-11-25 | 1985-01-08 | Thomson-Csf | Interferometer for the real time display of deformations of vibrating structures |
US4571080A (en) * | 1981-11-09 | 1986-02-18 | Thomson-Csf | Michelson interferometer with a photorefractive mirror |
US4542955A (en) * | 1982-06-18 | 1985-09-24 | Thomson-Csf | Device for illuminating an electro-optical medium for recording holograms in real time |
US4603096A (en) * | 1984-12-21 | 1986-07-29 | Agency Of Industrial Science & Technology | Hologram recording material |
US4788428A (en) * | 1985-03-04 | 1988-11-29 | The United States Of America As Represented By The Secretary Of The Navy | Thermodynamics infrared imaging sensor |
US4987545A (en) * | 1986-05-20 | 1991-01-22 | Ingegerd Dirtoft | Method for monitoring the manufacture of a product |
DE3720142A1 (de) * | 1987-06-16 | 1988-12-29 | Rottenkolber Holo System Gmbh | Holographische messeinrichtung |
US5049963A (en) * | 1989-03-24 | 1991-09-17 | Matsushita Electric Industrial Co., Ltd. | Holographic television apparatus with semiconductor device |
US5410406A (en) * | 1993-02-01 | 1995-04-25 | Holographics Inc. | Method and apparatus for nondestructive inspection utilizing phase integration and recording of induced vibrating nodal patterns |
US5479257A (en) * | 1993-04-05 | 1995-12-26 | Olympus Optical Co., Ltd. | Method of and apparatus for detecting object position using a fourier transform of the object image and processing system using the same |
US5827971A (en) * | 1996-05-31 | 1998-10-27 | Lockheed Martin Idaho Technologies Company | Optical vibration detection spectral analysis assembly and method for detecting vibration in an object of interest |
US5684588A (en) * | 1996-10-04 | 1997-11-04 | United States Of America As Represented By The Secretary Of The Air Force | Homodyne and hetrodyne imaging in a light scattering medium |
US6246521B1 (en) | 1996-11-05 | 2001-06-12 | Thomson-Csf | Compact lighting device |
US6134006A (en) * | 1998-02-25 | 2000-10-17 | Becthel Bwxt Idaho, Llc | Imaging photorefractive optical vibration measurement method and device |
US20070052969A1 (en) * | 2003-09-26 | 2007-03-08 | Thales | Sensor device used to detect interferometric rotational speed and comprising an optical fibre |
US7489404B2 (en) | 2003-09-26 | 2009-02-10 | Thales | Fiber-optic interferometric rotation speed sensor including a non-linear mirror |
Also Published As
Publication number | Publication date |
---|---|
DE2812956C2 (de) | 1988-07-07 |
JPS53119078A (en) | 1978-10-18 |
FR2385079B1 (de) | 1981-12-11 |
GB1599966A (en) | 1981-10-07 |
DE2812956A1 (de) | 1978-10-12 |
FR2385079A1 (fr) | 1978-10-20 |
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